is the return line REALLY necessary?

[sflsurfrider]

what is the return line actually for?

im guessing that it bleeds the air out of the carb(s).

but, other than that, cant it be capped off? i can swear ive heard of this being done before.

anyone know for sure?

 

[DAG]

sorry dino

 

[WFO Speedracer]

I would think it would jack up the fuel pressure if you blocked it off,how about a oneway valve hooked to the return and plumbed back into the feed line to the carb making it a constant loop? Something like a jetworks valve but using less pressure.

 

[sflsurfrider]

I would think it would jack up the fuel pressure if you blocked it off,how about a oneway valve hooked to the return and plumbed back into the feed line to the carb making it a constant loop? Something like a jetworks valve but using less pressure.

its funny that you say that because the reason im asking is thats exactly how my whaler was plumbed from the factory (minus the checkvalve.... i think.... it looked like a fuel filter with three penises.

anyhoo..... maybe im nuts, but im not comfortable with that setup.... too many different pressure/suction things happening there..... how do you ensure proper suction from the tank when its easier to rotate a "loop" through the carb and its bypass?

 

[WFO Speedracer]

its funny that you say that because the reason im asking is thats exactly how my whaler was plumbed from the factory. maybe im nuts, but im not comfortable with that setup.... too many different pressure/suction things happening there..... how do you ensure proper suction from the tank when its easier to rotate a "loop" through the carb and its bypass?

If it is a loop like we are talking about it is still providing the same suction from the tank,if there is suction on the return line it still must be pulled completely through the carb.I have a setup on one of my boats where the return line goes into a large T fitting that the vent runs off of, never had any problems with that set up.

 

[sflsurfrider]

If it is a loop like we are talking about it is still providing the same suction from the tank,if there is suction on the return line it still must be pulled completely through the carb.I have a setup on one of my boats where the return line goes into a large T fitting that the vent runs off of, never had any problems with that set up.

teeing the return in with the vent line is different than teeing the return with the feed line.

the goal of the first one is being achieved due to like purposes. in this case, sending matter back to the tank, be it air or fuel.

the second scenario involves both suction and pressure.... two opposing forces. my thought is that its easier to recirculate air and a little fuel around this loop and it is to draw fuel from the tank, thus leaning out the engine at startup and making it run away.

i know i could just use the choke, or install a primer (as a band aid), but my question remains...... what happens if the return is completely blocked off

 

[WFO Speedracer]

It jacks up the fuel pressure which means you would have to change the popoff pressure to compensate,that might be a hard one to get tuned properly.

 

[#ZERO]

The return restrictor orifice acts like a fuel pressure regulator and also allows air bubbles to bleed off back to the fuel tank.

Most Mikuni fuel pumps are capable of putting out more fuel pressure but with this small return hole they are limited to around 2.5 psi at idle and 4.5 psi at high rpm.

If the pressure ever becomes higher then the pop-off pressure, precise fuel metering will become impossible.

I'm testing a new setup right now that uses an in-tank electric fuel pump and a 1/4" flow control valve set to a constant 6 psi.

The pump will flow about 130 Liters of fuel per hour and draws less current than your typlcal bilge pump.

 

[DAG]

i just dont like the idea of putting electrical wires in my gas tank:cool2:



sry no mor :spam:

 

[sflsurfrider]

ive seen the chitty kawi metal fuel taps as found in the TS and SC completely crystalize and block the return 100%.

neither one had any fuel problems.

not saying that youre wrong or anything like that... just wondering if it would truly "lower" the popoff. i could see how it could.

 

[sflsurfrider]

i just dont like the idea of putting electrical wires in my gas tank:cool2:



sry no mor :spam:

there are more than likely wires in the fuel tank of your car.

 

[#ZERO]

i just dont like the idea of putting electrical wires in my gas tank:cool2:

Go and check the wires going into your fuel tank on the car you're driving.

In-tank fuel pumps are pretty common on most automobiles these days.

 

[WFO Speedracer]

I am all for the try it and see approach,thats what I usually do ,sometimes it works out,sometimes it doesn't,one thing is for sure you will learn something from it be it right,wrong or otherwise.

 

[DAG]

good points,, i stand corrected

 

[waxhead]

Im not sure why you are trying to do that to your tank
Are you having a fuel issue you cant get past

 

[WFO Speedracer]

Most boat tanks do not have fuel return line fittings installed,thats my assumption here and is also why I ran my return line into a T fitting on the fuel tank vent.

 

[vitaly]

what is the return line actually for?

im guessing that it bleeds the air out of the carb(s).

but, other than that, cant it be capped off? i can swear ive heard of this being done before.

anyone know for sure?

Please bear with me, I'm too busy and tired right now to completely follow the thread, but I asked myself the same question while looking at the single carb setup last night. I actually suggested blocking the line instead of replacing the rotten hose.
Anyway, bookmarking this thread... just in case...

 

[sflsurfrider]

Im not sure why you are trying to do that to your tank
Are you having a fuel issue you cant get past

not having a fuel issue. my boston whaler (yami 701) uses regualar boat tanks. boats typically dont have a return as they dont use a pwc-type fuel pumping system. the have float chambers like carbureted cars = no return.

i 'could' put a return line on the tank, but since have 2 tanks, id need to put 2 return lines..... and a divertar valve (on/res) between the carb return and tanks and switch depending on which tank im drawing from. otherwise id quickly drain one tank into another, through the return line, and overflow a tank or 2.

 

[#ZERO]

Im not sure why you are trying to do that to your tank
Are you having a fuel issue you cant get past

If you've ever hooked up a fuel pressure gauge between a conventional Mikuni fuel pump and return restrictor you'll see how crazy the fuel pressure responds to fluctuating idle changes.

Mechanical fuel pumps are prone to problems and rely on a steady pulse signal for them to operate properly.

Most modified engines start to loose the pulse signal to the fuel pumps at higher rpms and the diaphragms in the fuel pump can't react fast enough.

Electric fuel pumps supply a constant amount of flow and pressure depending on the voltage and are starting to be more common on jet-skis & jet-boats with 2-stroke engines for more accurate fuel metering.